The present invention relates to airbag apparatuses and folding methods for airbags that unfold and inflate about an occupant in response to an impact exceeding a predetermined level applied to the body of a vehicle, thus reducing the impact acting on the occupant.
Conventionally, an airbag apparatus includes a gas generator and an airbag that is unfolded and inflated by the gas generated by the gas generator. The gas generator has an inflator for generating the gas and a retainer for fixing the inflator. The airbag may be shaped in different manners depending on positions at which the airbags are installed. For example, Japanese Laid-Open Patent Publication No. 2001-114060 describes a side airbag apparatus including a flat airbag. The airbag is formed in a bag-like shape by folding a panel sheet in two and sewing the circumference of the panel sheet.
In an airbag apparatus, at least the inflator of the gas generator must be arranged in the airbag for unfolding and inflating the airbag by the gas. For this purpose, the airbag is fabricated according to the following steps. First, the circumference of the panel sheet is sewn except for a portion of the circumference that defines an insertion opening through which the inflator is inserted into the airbag. The inflator is then installed in the airbag through the insertion opening. Subsequently, the portion corresponding to the insertion opening, or the non-sewn portion of the circumference of the airbag, is sewn. The insertion opening is thus closed.
For facilitating installation of the gas generator in the airbag, such as insertion of the inflator and the retainer into the airbag and connection of a harness to the inflator, the insertion opening must be relatively large. The insertion opening is made visible from a side of the airbag. Therefore, if the insertion opening remains open, an excessive amount of gas may leak from the insertion opening when the airbag is unfolded and inflated. In this case, the airbag cannot be inflated to a predetermined interior pressure. In order to avoid this, the airbag, the flat type in particular, must be subjected to post treatment of the insertion opening following the sewing step of the panel sheet. In the post treatment, the insertion opening may be closed or reduced in size by sewing the circumferential portion of the airbag corresponding to the insertion opening or blocked by folding the circumferential portion of the airbag corresponding to the insertion opening.
That is, fabrication of the flat airbag requires three steps, sewing the circumference of the panel sheet, installing the gas generator, and performing the post treatment. The production efficiency for the airbag is thus relatively low. Further, although the inflator is received in the airbag, the harness must be projected from the insertion opening to the exterior of the airbag. Therefore, even after the post treatment, a portion of the insertion opening must be maintained open, making it likely for the gas to leak from the open portion. It is thus difficult for the flat airbag to maintain the interior pressure after the airbag is unfolded and inflated. Further, if the circumferential portion corresponding to the insertion opening is sewn in close vicinity to the harness for maximally closing the insertion opening in the post treatment, problems such as damage to the harness or short circuiting of the harness may occur.